body clock

E-books ‘damage sleep and health,’ doctors warn.

Posted by

0


Reading under the sheets

If you curl up under the duvet with an e-book for a bedtime read then you are damaging your sleep and maybe your health, US doctors have warned.

A team from Harvard Medical School compared reading paper books and light-emitting e-readers before sleep.

They found it took longer to nod off with a back-lit e-reader, which led to poorer quality sleep and being more tired the next morning.

Original Kindle readers do not emit light so should be fine, say experts.

Experts said people should minimise light-exposure in the evening.

Whether you are perusing the Man Booker shortlist or leafing through Zoella, the impact of reading on your sleep is probably the last thing on your mind.

But there has been growing concern about the dangers of light before bedtime.

Body clock

Our bodies are kept in tune with the rhythm of day and night by an internal body clock, which uses light to tell the time.

But blue light, the wavelength common in smartphones, tablets and LED lighting, is able to disrupt the body clock.

Blue light in the evening can slow or prevent the production of the sleep hormone melatonin.

Book vs ereader

Twelve people were locked in a sleep laboratory for two weeks.

They spent five days reading from a paperback and five days from an iPad.

Regular blood samples showed the production of the sleep hormone melatonin was reduced by reading an e-book.

People also took longer to fall asleep, had less deep sleep and were more tired the next morning.

The researchers said other e-readers such as the Nook and Kindle Fire produced similar wavelengths of light and would have the same impact.

The findings were published in the journal Proceedings of the National Academy of Sciences.

‘Concern’

Lead researcher Prof Charles Czeisler told the BBC News website: “The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book.”

He said disrupting sleep in turn affected health.

“Sleep deficiency has been shown to increase the risk of cardiovascular disease, metabolic diseases like obesity and diabetes, and cancer.

“Thus, the melatonin suppression that we saw in this study among participants when they were reading from the light-emitting e-reader concerns us.”

Sleep hygiene

Dr Victoria Revell, who researches the impact of light on the body at the University of Surrey, told the BBC: “This is a very good study and I think it’s really interesting.

“We should be advising people to minimise their [light-emitting e-reader] use in the evening, particularly teenagers who are a group that are using their phones and tablets late in to the evening.”

Teenagers naturally have a late body clock, which makes them slow to rise in the morning and up late at night.

“People who already have a delayed body clock are delaying themselves much further and that is a very important message,” Dr Revell added.

Prof Czeisler agreed, saying there was “special concern” for teenagers who were already sleep deficient by being forced to get up early for school.

Study reveals why the body clock is slow to adjust to time changes.

Posted by

0


New research in mice reveals why the body is so slow to recover from jet-lag and identifies a target for the development of drugs that could help us to adjust faster to changes in time zone.

With funding from the Wellcome Trust and F. Hoffmann La Roche, researchers at the University of Oxford, University of Notre Dame and F. Hoffmann La Roche have identified a mechanism that limits the ability of the body clock to adjust to changes in patterns of light and dark. And the team show that if you block the activity of this gene in mice, they recover faster from disturbances in their daily light/dark cycle that were designed to simulate jet-lag.

plane

Nearly all life on Earth has an internal circadian body clock that keeps us ticking on a 24-hour cycle, synchronising a variety of bodily functions such as sleeping and eating with the cycle of light and dark in a solar day. When we travel to a different time zone our body clock eventually adjusts to the local time. However this can take up to one day for every hour the clock is shifted, resulting in several days of fatigue and discombobulation.

In mammals, the circadian clock is controlled by an area of the brain called the suprachiasmatic nuclei (SCN) which pulls every cell in the body into the same biological rhythm. It receives information from a specialised system in the eyes, separate from the mechanisms we use to ‘see’, which senses the time of day by detecting environmental light, synchronising the clock to local time. Until now, little was known about the molecular mechanisms of how light affects activity in the SCN to ‘tune’ the clock and why it takes so long to adjust when the light cycle changes.

To investigate this, the Oxford University team led by Dr Stuart Peirson and Professor Russell Foster, used mice to examine the patterns of gene expression in the SCN following a pulse of light during the hours of darkness. They identified around 100 genes that were switched on in response to light, revealing a sequence of events that act to retune the circadian clock. Amongst these, they identified one molecule, SIK1, that terminates this response, acting as a brake to limit the effects of light on the clock. When they blocked the activity of SIK1, the mice adjusted faster to changes in light cycle.

Dr Peirson explains: “We’ve identified a system that actively prevents the body clock from re-adjusting. If you think about, it makes sense to have a buffering mechanism in place to provide some stability to the clock. The clock needs to be sure that it is getting a reliable signal, and if the signal occurs at the same time over several days it probably has biological relevance. But it is this same buffering mechanism that slows down our ability to adjust to a new time zone and causes jet lag.”

Disruptions in the circadian system have been linked to chronic diseases including cancer, diabetes, and heart disease, as well as weakened immunity to infections and impaired cognition. More recently, researchers are uncovering that circadian disturbances are a common feature of several mental illnesses, including schizophrenia and bipolar disorder.

Russell Foster, Director of the recently established Oxford University Sleep and Circadian Neuroscience Institute supported by the Wellcome Trust, said: “We’re still several years away from a cure for jet-lag but understanding the mechanisms that generate and regulate our circadian clock gives us targets to develop drugs to help bring our bodies in tune with the solar cycle.Such drugs could potentially have broader therapeutic value for people with mental health issues.”

Source: Cell.